In this study the DNA of selected human herpesviruses will be characterized and the DNA base sequence homologies among those herpesviruses investigated. Of particular interest are the oral and venereal strains of herpes simplex virus and several isolates of varicella-zoster virus. The method is to construct a DNA heteroduplex composed, for example, of one DNA strand from herpes simplex virus type 1 and the complementary DNA strand from herpes simplex virus type 2. The heteroduplex is mounted for observation in the electron microscope, along with appropriate length standards. Regions of sufficient homology will appear duplex. Regions of insufficient homology will exist as two unpaired single strands. Detailed physical maps of base sequence homology can be achieved. For cases in which the heteroduplex method cannot be applied for technical reasons, the degree of homology between two DNAs will be investigated by measuring the rate of Renaturation of one DNA in the presence of a second, radioactively labeled DNA. An attempt will be made to correlate the data obtained from this study with the oncogenic potential of each herpesvirus.